Forgotten Pasts
by ChillTaco
Summary: Papyrus wants to know what his Brother is hiding. With Undyne and Alphys, he goes on an investigation, but they might be too deep in over their heads. And who's the strange girl, Sans seems so attached to, who's her little sister? Who're all these people looking so much like alike of Sans and Papyrus? Many shadows must be uncovered. Two OCs and T to be safe, but not all the time.


**Hi! This is my first fanfiction and I've been thinking a lot about this story and using a lot of time on it so I really hope you like it! ;)**

 **If you do like it, feel free to use or write about it anytime, you want! n_n I just put it out here cuz I got an idea and then I was like (might as well sow the world it, and maybe somebody who's a better writer will find it and think "the idea is pretty good but it's gonna need a little help" and it becomes a pretty good fanfiction)**

 **I probably won't be very good at uploading frequently because I have school and a lot of homework and all the usual stuff, but I'll try!**

 **It would be cool if you would comment, if not feedback then just an emoji, a letter, a number or something so I know how many, if anyone at all, has read it, Thanks!**

 **I don't own Undertale or any of its characters, I only own Kira and Sophie. I don't own any of the other AUs either.**

 **I would also like to apologize for any spelling, or other mistakes. I'm "only" 12 and I started learning English around 1-2 years ago (I'm Danish), so I'll probably make way too many mistakes. (sorry** **)**

 **Also, Frisk and Chara does not exist in this fanfiction. Or maybe it's just before them.**

 **Happy reading!**

Chapter one

Papyrus was sitting by the table, next to sprinkles and eating spaghetti, when Sans came tramping down the stairs, muttering curse words, with an angry expression. As usual Sans wouldn't tell Papyrus what was wrong, but was just saying that he was "fine" every time Papyrus asked. "why won't you ever tell me anything?!" Papyrus blurted out. Sans' head jerked up in shock from Papyrus' outburst. "Bro, that's not true, I tell you almost everything" this just got Papyrus even more fired up "ALMOST everything?!" Sans figure seemed to shrink to almost invisible smalls, "well bro you know there's things you can't- Papyrus started to yell, while standing up "we are brothers aren't we, Sans, and brothers shouldn't keep secrets from each other! Or maybe you don't consider me your brother?!" Sans eye lit up and anger was forming in it "of course I consider you my brother, how could you say something like that!" Sans headed out the door and slammed it hard after him. Papyrus slowly sank back down on the chair and buried his head in his hands.

Papyrus called Undyne to tell her what happened, and she said that she would hurry over. When she arrived it was with Alphys and Mettaton by her side, "so you see I called Alphys and told her where I was going and she insisted on coming along, and then Mettaton just kind of followed" Papyrus just smiled and closed the door behind them "it's ok I don't mind. You guys want to watch some TV?"

The comic show they saw had everyone laughing and everything just felt right. Suddenly they heard something breaking outside so they stopped laughing, "What was that?" Undyne whispered, then Sans voice sounded through the window, "shh…! What if they hear you?" another voice, a girls voice, "they won't, they won't I just checked, they're laughing they're heads off in there" Sans voice again "really? Ok. Shit! How do you get blood off this jacket?" The girl sounded annoyed now "Jesus! I've told you like a thousand times already! You need to put it in cold water and then…" She blabbered off the rest of the instructions "you'll also need to bandage all of the ribs separately-" Sans voice was a little thin when he spoke again. "Well I remember THAT" the girl, her voice dripped in concern, spoke again. "You really should take better care of yourself" Sans was in full defense mode. "Hey, you got more than a little roughed up too!" now they were just bickering "well I don't lie to my family about it! Secrets is always a bad thing, and I know what you're going to say now -I don't have a choice you know I have to keep everything a secret- well that's not true, you could at least tell them some of the less important things!" deafening silence followed and then. "I'm sorry but I can't do that, if I tell Papyrus anything he'll tell it to Undyne and Undyne is going to have to tell it to king Asgore, if she doesn't want to commit treason and she somehow doesn't strike me as someone who would do that… I have to protect my brother. I have to protect the underground." After a long period of silence, the girl sighed "Goodnight Sans"

Sans came into the house, looking like none of that just happened. "Hi, look I'm sorry for being a complete jerk to you this morning, I'm just really stressed right now and I have a lot to worry about, so I overreacted and that totally wasn't ok" then Sans walked up the stairs to his room. When the door was closet behind him, everyone started yelling at the same time. "What the hell just happened" Undyne yelled "who was that and why didn't I recognize them?!" Alphys squealed "Ohh myyyy, what a scandal" Mettaton said. But Papyrus was just sitting there staring, speechless. "I don't understand" he said "why did Sans need to get blood of his jacket, and what kinds of secret is it that he haves?" Undyne looked concerned at Papyrus and said in a much calmer tone then normal "I don't know Paps, I really don't know" Alphys pushed her glasses longer up on her nose "T-this is quite serious, m-maybe we should, j-just, y-you know w-watch him, l-like just t-tomorrow or s-something?" Undyne looked thoughtful at her "yes that does sound like a good idea. We might have to do that until we find a good solution." Mettaton looked surprised at them "I don't want to get involved in some espionage or some other crazy stuff! I'm out!" Papyrus looked at Mettaton "that's ok. We won't force you into anything, if you don't want to. I think I'm in too, though." Undyne grabbed Papyrus and Alphys' shoulders "we're the best team ever! Sans won't be able to keep ANY secrets from us!" Alphys wanted them to agree on a certain time to meet. After some discussing back and forth they all agreed on Papyrus to call them when he supposedly headed out to work. Everyone left.

Later around dinnertime, Papyrus headed out to the kitchen to heat up some premade spaghetti. His brother came into the room, his stomach growling, which didn't really make sense considering, they didn't have stomachs. "Heeeeyyyy what'cha making bro?" Sans jumpslided onto the kitchen table "smells dilissssh!" Papyrus grabbed two plates and splashed the spaghetti onto it "well why don't you come and taste for yourself?" Sans grabbed both the plates along with some cutlery and two cups. He was so lazy he didn't even prepare the table without blue magic. Papyrus took off his apron and hang it on a hook next to the fridge. Both brothers sat down at the table next to sprinkles. Sans consumed his food so fast and animalistic, it almost made Papyrus laugh. Almost. He did choke on his food though, and Sans was at his side in a matter of milliseconds and gently patted him on the back "you ok bro?" Sans gave him some water and then he was ok again. "I'm fine brother, I'm fine." The rest of the meal they talked about unimportant stuff and about Sans terrible jokes, and laughed like usual. Sans read Papyrus his bedtime story and then they both went to sleep.

Next morning Papyrus woke up around five like usual. He did his normal morning routine, right before he headed out the door he woke up Sans, and told him he was leaving, like usual.

When Papyrus was out in the snow, he took out his phone and looked at it for a good solid five minutes. He remembered Sans' hand on his back gently patting, about Sans' eternal concern for him… No, it had to be done, he needed to know what Sans was hiding, he was tired of Sans' lies and silence. There'd be no more secrets. He pressed call.

Undyne and Alphys arrived together, they had probably already been together when Papyrus called. Papyrus waved and the duo hurried over. They didn't exchange many words; Papyrus said that Sans was probably in his room so that'd be where they should spy, and other than that just hello's and all that. They looked into Sans room through the window. Sans was sitting on the bed with his shirt off, he had three big slashes across the ribs. The slashes were bleeding lightly and Sans was, calmly, bandaging the wounds. Suddenly they were all blinded by a glimpse of light, but from their position, they couldn't see where the light came from. At once Sans started talking, a slight smile on his face. Then he laughed. Papyrus hadn't seen him laugh like that for a long time, and it reassured and concerned him at the very same time. Suddenly another glimpse of light, where everyone pinched together their eyes, and then Sans was gone. Just like that. "What. The. Hell. Just. Happened." Undyne was standing, looking at the very spot Sans should have been, if not for the weird glimpse of light. By now, living with his brother for that long, Papyrus really wasn't as surprised as the others, weird things always happened to brother, and he always seemed like he might be a little deeper than he let on. Alphys looked like she was thinking about something very interesting. Undyne was just hella confused!

The next day Papyrus, Undyne and Alphys was taking a comfortable stroll in the woods. They were patrolling the area of humans. Papyrus didn't really feel like spying on his brother had helped, if anything it had just left him with even more questions than before. Whom was that mysteries girl Sans had been talking to, the other day? Whom had he been talking to in his room? The same girl? Himself? No Sans didn't really strike Papyrus as a person who would talk to himself. On the other hand, Sans hadn't really struck him as a person who would keep secrets to his family either. And those slashes! Papyrus might not have known much about this whole situation, but he did know that Sans shouldn't have been hiding those. Papyrus was so buried in thought that didn't even notice the little yellow flower, hiding in the snow. "Papyrus! My friend! How have you been?" the little flowers expression was as sweet as honey and sugar, but Papyrus knew that, Flowey could actually be a real meanie despite the cutie look. "Flowey. I've been fine thanks." He didn't really want anything to do with this flower, but he couldn't just leave and Flowey knew that. "Won't you stay a bit and hang out, Papyrus?" Or maybe he could. "I'm sorry Flowey, but I'm kinda busy at the moment." Papyrus started walking and his friends followed him. Suddenly something grabbed his ankle, painfully, and he fall as long as he was, flat on his face. "What the hell?!" Undyne stepped up to the small looking flower and stared at it. "What do think you're doing!?" She made a spear appear in her hand, and swung it, deflecting the attack, right as Flowey lashed out for her. She threw he spear at him, with overwhelming speed and strength. Flowey didn't even attempt to dodge. He started growing, bigger and bigger. Taller and taller. Long thorny roots shoot out of the ground, Floweys figure soon blocking the sun, creating new dark, threatening shadows. Suddenly, a fast blue blur, shoot seemingly out of nowhere. The blur raised his hand and a wall of blue bones appeared, the blur whipped his wrist and the bones shoot out towards Flowey, hitting him hard on the stem. "Is that really the best you can do trashba- what!? This isn't normal, is-is it some kind of poison… interesting." Then Flowey whipped out two roots, each coming from a different direction, towards… Sans! Papyrus yelled a warning filled with panic, but Sans easily jumped over and ducked under both roots. Suddenly a burning pain shoot up from Papyrus' leg and he cried out in pain. Sans head whipped around toward him, losing his focus on the flower. Flowey saw this as his peak to attack, and grabbed one of Sans' shinbones, hurling him into a tree. Sans knee seemed out of joint as he grunted in pain. Sans summoned a gasterblaster with a raise of his arm. He closed his fist and the gasterblaster released a beam of light and magic. Sans was huffing out of pain and was gasping for his breath, he kept summoning row after row of bones, firing gasterblaster after gasterblaster. By this time Undyne had adjusted to Sans' coming out of nowhere, and was now shielding him from Flowey, blocking attack after attack. Alphys was by Papyrus' side examining his wound. For the first time since Papyrus had met Flowey, he almost seemed…weak. Something caught Papyrus' eye. It was…a human girl looking very angry, inside… a very big cloud of smoke, shaped like… a dragon. The girl had long black hair that was at that moment whipping behind her. She was wearing a red headband, though Papyrus didn't think it looked like it helped much, and her bangs reached almost all the way down to her eyes. The girl was wearing baggy grey pants that only reached to right under her knee. She was wearing a matching grey top that showed belly, under it, could just be seen the strops of a black smaller top. Over the tops, she was wearing a long, green, baggy cardigan with hood, so long in fact, that it reached under the end of her pants and all the way to the middle of her shin, almost all the way down to her long black military boots. She was flying; she was inside the dragon's mouth, which now was in an angry roar. The girl angrily yelled Sans name, she sounded strikingly alike of the girl, they had heard talking with Sans, outside, the other day. Sans cursed colorfully. He jumped up from the place he was sitting snapping the knee back with a groan and the green magic of healing dancing around his fingers. Sans had looked hurt, like he couldn't stand. Like his leg hurt so much that he couln't just snap it back and heal whatever was broken. The way Papyrus would feel if, HIS leg went out of joint! How many lies was Sans gonna make?! The girl landed on the forest floor with a loud thump. Out of the corner of his eye, Papyrus saw Flowey disappear into the ground. The girl opened her moth, and out came a burst of fire and flames. Sans summoned a big gasterblaster in front of him, so the fire wouldn't hit him. "Goddamn it Kira! I don't wanna fight you! Sans was yelling now. The girl took off from the ground, anger pulsating from her small stature. "Then MAYBE you shouldn't have invaded my privacy, opened doors that should never have been opened, and you didn't even close it after yourself. You IDIOT!" She summoned the head of her smoke dragons with a raise of her arm and fired it by closing her fist, not unlike the way Sans handled gasterblasters. "I didn't think, I only felt bad. Because I hadn't killed him. I had banished to a world only filled with pain. I thought that maybe it would be easier for him, if I just…ended it, ended him." Sans summoned a wall of bones taking the fire head on. "What made you think, that he deserved it?!" The girl stretched her open hand out, turning op against the sky, and then she wrenched it higher up, making spikes tune out of the ground everywhere that Sans was standing. Sans started running, and then he jumped upwards, but the weird thing was that he didn't go down again he just kept floating upwards. He summoned three gasterblasters one floating right under him, and the two others on each side of him. Sans fired the two on the side, his blue untied sneakers landing on the skull under him. The girl easily blocked his attack, but then when she started gathering magic in her palm, she suddenly fell to the side, all magic gone. Sans dived, all his magic gone as well, after her, yelling "Kira!" which seemed to be her name. For a split second, Papyrus was sure that his brother wouldn't catch Kira, but right before impact with the ground Sans caught her in his arms. People started running, even Papyrus himself, towards Sans and the girl, Kira. Sans was sitting on the ground with the human girl in his arms, a worried look on his face, yelling her name, shaking her. Before any of them could reach them, Sans picked up the girl and started carrying her into the woods, the others followed not knowing what to do. Undyne suddenly said that they should capture the human, Papyrus asked what was going on and Alphys asked where they were going, but Sans just ignored them all.

After a long time of walking, they came to a big forest glade. Sans walked into the glade. Across from them, at the edge of the glade, next to the trees, was a small tidy looking house. Suddenly the doors to the house flew open, smashing into wall, and out came a little, light brown haired, human girl. She couldn't have been more than a few years old. Her hair, tidied up in two long twintails, tied with green ribbons, the same color as the light green summer dress she was wearing, over a long white blouse. "Sans! Sans! Kira! Kiiira! Come inside! Hurry up!" The girl was a few feet away, when Undyne summoned a spear, pointing it at the girl. "Go ahead," Sans said, a gasterblaster already floating behind him "but know that, I'll toast you, if you try." Alphys looked worried at Sans, eye sockets empty and she whispered something in Undynes ear. Undynes spear disappeared and Sans' head whipped around, towards the small girl. "Sophie," he said "she just suddenly passed out; I don't know what's wrong!" The girl, whose name was apparently Sophie, looked a lot calmer than before "Ohh… that, well that's been happening sometimes lately, I'm worried, but at least I know that she's going to wake up again. I'm just happy that you're still alive! Come on let's get her inside." The two of them shuffled Kira inside, and laid her on a table. The girl per routine checked for wounds and heartbeat, and then she poured some kind of green liquid into Kira's mouth. "Sans can you please lay her into her bed, all we can do now is wait and give her time to rest" Sans just nodded and lifted up Kira, carrying her into another room. The girl turned toward the three of them "heh… I don't expect Sans to have told ya 'all very much, so come on let's go into the living room." The girl walked a few feet to the door, opened it and stepped into a small tidy living room. It was clean, with a wide window across from them, two sofas, on each side of the room, with a dining table between them, (apparently also their dining room) a big pine bookshelf behind one sofa and one more window behind the other.

The girl sat in one of the sofas and all three of the huddled on the other one. "My name is Sophie, and I'm eight years old. I'm Kira's 13 years younger sister. So yeah, my sister is the same age as Sans. We are friends with Sans." They all looked at her in a couple of minutes, not knowing what to say. Sophie got up in one motion, repeatedly wiping her sweaty hands in her dress. "Would you like some tea? Coffee? I'll go make some of each." and then she was gone. The door opened and in came Sans with an exhausted look on his face. Sans was bombarded with questions as soon as he entered the room. "Brother? Why didn't you tell me about those humans?!" Sans walked over and sat in the sofa Sophie had been sitting in, minutes ago. "Look Papyrus, I'm sorry that you had to have find out this way, but I'm, not sorry for not telling you. It was my only opportunity. I had to protect you; I had to protect the underground. I had to." Undyne suddenly yelled "Sans! I don't understand, you have to capture the humans, don't you wanna go to the surface?!" Sans rubbed his temples and sighed "Undyne it's not that simple-". Undyne got up and summoned a spear "You are committing treason Sans! If you don't have the guts to do this then I will!" Undyne took a step toward the kitchen, and suddenly the room was filled with gasterblasters all pointing at Undyne. "Undyne stop, I will not allow that- actually I forbid it! Now put away that spear!" Undyne looked at Sans, her eyes filled with disbelief and betrayal. "Why! Sans just tell us why! You explain nothing, nothing at all!" Sans slammed his skeleton hands, down onto the table and shouted, "Because they are not humans and because it will not break the barrier even if you have a hundred human souls! It will not work!" Everyone looked astonished at Sans. Then Sans said in a much calmer voice, "look we haven't been honest with you. Right from the start, we lied. It isn't true, that you can break the barrier with seven human souls. No matter how many human souls you have, you won't be able to break the barrier." Everyone looked confused. Especially Undyne. She was too smart to not understand what they were talking about, but she wasn't as smart as Alphys, to understand so much that she could think of an intelligent question. "Uhh… I don't understand." Alphys looked at Sans for a very long time, and then she asked the question none of the others had thought yet. Yet. " So… putting aside the question about how you have that kind of power, then why? Why would you lie to us? Is there a way, or is it just over, should we just give up?!" For the first time since Papyrus had meet Alphys, she was raising her voice, and not stammering. Sans sighed again, a pained expression on his face "We were trying to prevent you from going to the surface. The underground may be cramped and slightly claustrophobic, but it's like heaven compared to the hell up there! There's a full on war up there. The humans call it "The third world war". They are slaughtering each other, their own race! You expect them to welcome US?! If they knew we still existed, they would send one of their bombs. Those bombs can devastate an entire city by blast, fire, and radiation. A bomb like that would destroy all of Mount Ebott. and everything under, and around it! There are only about 4 billion left of the human race! Maybe when they are extinct, but there will probably be so much radiation that it will take a lot longer." Alphys tilted her head, it was too much to process, she just had to move on to the next point. "T-then how D-DO you b-break the b-barrier?" Sans was looking at her in a funny way. Then he said, "I guess I might as well tell you, it won't help you get out of here, just knowing how to. The only way to break the barrier is by combining a human soul and a monster soul." Alphys looked truly confused. At that moment Undyne broke into the conversation, "Like when a monster absorbs a human soul?" She sat down on the couch again. "No," Sans said "it's actually more like literally fusing the two souls together, but as you already know, it's impossible without killing both souls, human as well as monster, so it should indeed have been impossible.

Crash!

Ouch! That hurt! Everyone whips their heads around to the sound of a deep male voice.

Sans quickly got up.

"Was that…?"


End file.
